The presence of dispersed liquid carcinogens and chemical agents on natural surfaces such as soil and sand pose considerable risk to unprotected personnel. Development and application of a standoff detection technology that can sense contaminants on/within terrestrial and manufactured surfaces through their infrared (IR) absorption/emission signatures would allow personnel to protect themselves and take the appropriate action to decontaminate, or to avoid the contaminated areas altogether. It is therefore an object of this invention to provide this capability.
When IR-absorbing liquids are dispersed on sand and soil surfaces in low quantity, their molecular absorption resonant peaks are revealed from a Fourier Transform Infrared (FTIR) spectroradiometer as the surfaces undergo external heating by a laser beam source or other suitable beam source irradiation. Furthermore, the laser dwell time of an isotopic CO.sub.2 laser beam required to elevate surface temperature for target (target and contaminant are synonymous (identification is lower when the irradiating beam is polarization-modulated.
In the early 1906's, the U.S. Army Chemical Systems Laboratory (now known as the U.S. Army Chemical Research, Development, and Engineering Center or CRDEC) had started various remote sensing programs for detecting threat chemical and biological agents in vapor cloud, aerosol, rain, and surface contamination scenarios. Short-path IR point sensor and spectral filter wheel devices were the first evaluated. A need for passive spectroscopic techniques that collect and process radiance from natural or preexisting sources was identified in the early 1970's and advanced development on the U.S. Army's field remote chemical agent detection unit, denoted as the XM21 unit was underway in 1979. The technology the XM21 instrument was based on originated from the famous Michelson-Morley experiments, published in 1887. Modern active systems that provide a coherent and highly directional laser source with which to irradiate a target for identification started with Raman studies in the mid to late 1970's. (The Raman effect was first predicted in 1923 by Adolf Smekal and observed experimentally in 1928 by Chandrasekhara Vankata Raman.) In addition, research started in the early 1980's on applying laser induced fluorescence and DISC/DIAL, (Differential Scattering/Differential Absorption LIDAR--Light Detection and Ranging) technologies for remote chemical/biological detection. DISC/DIAL devices show the most promise, and are the most technologically advanced vapor detection and range resolve systems currently in operation.
While some instruments exploiting the above technologies are successful in detecting specific vapor agent clouds and their simulants in the open atmosphere at low concentration lengths and at ranges in the kilometers, a reliable technology to sense ground contaminants below mass densities proven harmful to life is not yet known to have been developed.
It is therefore still another object of the present invention to provide a system which proves a capability for detecting chemical agent simulants DMMP (Dimethyl methyl phosphonate), DIMP (Diisopropyl methyl phosphonate), or SF96 (polydimethyl Siloxane, a long chain silicon base oily liquid of low vapor pressure) applied to soil and sand surfaces, in .about.0.3 ml (droplet) quantity or below.
Other objects and advantages will appear hereinafter.